New fluorine-18 labeled benzaldehydes as precursors in the synthesis of radiopharmaceuticals for positron emission tomography

4,5-Bis(butoxy)-2-nitrobenzaldehyde and 4,5-bis(tert-butoxycarbonyloxy)-2-nitrobenzaldehyde, as well as their fluorine-18 labeled derivatives (the half-life of F¹⁸ is T_1/2 = 110 min) were synthesized for use as precursors in the synthesis of fluorine-18 labeled catecholamines and 6-[¹⁸F]fluoro-l-DOPA ((S)-3-[4,5-dihydroxy-2-[¹⁸F]fluorophenyl]-2-aminopropionic acid), important radiopharmaceutical agents (RPAs) for positron emission tomography. An advantageous feature of the newly obtained substituted nitrobenzaldehydes is the presence of labile protective groups which can be removed without using aggressive chemicals and severe conditions, which is of fundamental importance for automation of the RPA synthesis in modern synthesis apparatus. A high and stable radiofluorination yield achieved under the optimum fluorination conditions (Kryptofix 222 [K/K2.2.2.]⁺[¹⁸F^–], DMF, 140 °C, 10 min) using 4,5-bis(butoxy)-2-nitrobenzaldehyde as a substrate (83±6%, the number of experiments was n = 15) makes this compound a precursor of choice for the radioactive synthesis.